Unlimit tiles amount

Hey guys! Im having a little problem. How can I increase a limit from a setting called tiles in the perfornmance window. I need to speed up my renders that way.

For CPU tile size of around 16x16 seems to be the fastest one. The minimum is 8x8, why would you want to go smaller than that? Anyway, with optimizing the tile size for your device you can shave only couple of percent off from the render timeā€¦